With emergence of services in communication networks, increased communication capacity of data is today required by end users. The end users use UEs to communicate data in basebands with radio base stations in radio access networks. In order to face the required increased communication capacity, modern radio base stations have been developed which are capable to use and handle basebands which comprise multiple frequency bands when communicating data according to various services.
The frequency bands are defined and assigned by authorities, e.g. the EBU (European Broadcasting Union), to operators of the communication networks and the operators decide which frequency bands that will be used by the UEs.
In this description, the term “User Equipment” (UE) will be used to denote any suitable communication terminal adapted to communicate with a radio base station. A UE, may be implemented as a mobile phone, a PDA (Personal Digital Assistant), a handheld computer, a laptop computer, etc. A “radio base station” may be implemented as a NodeB, an eNodeB, a repeater, etc.
The frequency bands which are assigned to the UEs or radio base stations for their communication are separated in the frequency plane. For widely separated frequency bands, e.g. separated as much about 1 GHz from each, the UEs have specific functionality for handling the separated frequency bands. Some examples of such functionality will be described below.
The FIG. 1 which is a schematic graph illustrates a situation where two frequency bands A and B are separated with 1 GHz, e.g. a frequency fA of the frequency band A is 1 GHz lower than a frequency fB of the frequency band B.
In order to make use of widely separated frequency bands receivers are commonly designed with double receiver branches, which will be described below with reference to the FIGS. 2 and 3.
FIG. 2 is a schematic block diagram which illustrates an arrangement in an FDD (Frequency Division Duplex) double band receiver 200.
An RXRF (Receiver Radio Frequency) signal spectrum which comprises a lower frequency band and a higher frequency band is received at an antenna 202. The frequency bands are separated and handled by two respective branches of the receiver 200. The lower frequency band with a centre frequency of fA is handled by the upper branch of the receiver 200, and the higher frequency band with a centre frequency of fB is handled by the lower branch of the receiver 200. In addition, four graphs are illustrating the situation at four positions of the branches, which will be further described below.
When the RXRF signal spectrum has been received by the antenna 202, a set of band-pass filters 204 are arranged to divide the RXRF signal spectrum into the two branches, i.e. to separate the RF upper and lower frequency bands. The lower RF frequency band and the upper RF frequency band are amplified with respective LNAs (Low Noise Amplifiers) 206, and are further filtered by respective RF filters 208. Commonly, respective adjustment means 210 are arranged to adjust the power levels of the respective RF frequency bands. The RF frequency bands are frequency shifted into corresponding IF (Intermediate Frequency) frequency bands by RF Mixers 212, which are arranged in the respective branches. The input signal to the upper mixer 212 is illustrated in the upper right graph, where the lower frequency band with a frequency fA and an LO (Local Oscillator) output signal floA are seen. The resulting output signal of the upper mixer 212 is illustrated in the upper left graph, where the lower frequency band with the frequency fA_IF is seen.
Correspondingly, the input signal to the lower mixer 212 is illustrated in the lower right graph, where the upper frequency band with the frequency fB and another LO output signal floB are seen. The resulting output signal of the lower mixer 212 is illustrated in the lower left graph, where the upper frequency band with the frequency fB_IF is seen.
Commonly, the IF frequency bands of the branches are further filtered by IF band-pass filters 214, 218, and power adjusted by level adjustment means 216 before being feed into A/D converters 220 to be converted into a first frequency band and a second frequency band of the baseband.
If the receivers handle multiple frequency bands which are located closer to each other, the frequency bands are commonly handled by one single branch, which will be described below.
FIG. 3 is a schematic block diagram which illustrates an arrangement in an FDD (Frequency Division Duplex) double band receiver 300.
An RXRF (Receiver Radio Frequency) signal spectrum which comprises a lower frequency band and a higher frequency band is received at an antenna 302. A difference when compared with the double band receiver of FIG. 2 is that the two frequency bands fA and fB are handled by one and the same branch of the receiver 300. In addition, two graphs are illustrating the situation at two positions of the receiver 300, which will be further described below.
When the RXRF signal spectrum has been received by the antenna 302, a set of band-pass filters 304 are arranged to extract an upper and a lower RF frequency bands, i.e. the two frequency bands fA and fB. The lower RF frequency band and the upper RF frequency band are amplified with an LNA 306, and are further filtered by respective RF filters 308. Commonly, an adjustment means 310 is arranged to adjust the power levels of the RF frequency bands. The RF frequency bands are frequency shifted into corresponding IF (Intermediate Frequency) frequency bands by RF Mixer 312. The input signal to the mixer 312 is illustrated in the right graph, where the upper and lower frequency bands with the frequencies fA and fB and an LO (Local Oscillator) output signal flo is seen. The resulting output signal of the mixer 312 is illustrated in the left graph, where the lower and the upper frequency bands with the centre frequencies fA_IF and fB_IF are seen.
Commonly, the IF frequency bands of the branches are further filtered by IF band-pass filters 314, 318, and power adjusted by level adjustment means 316 before being feed into an A/D converter 320 to be converted into a first frequency band and a second frequency band of the baseband.
To be able to reconstruct the frequency bands into a receiver baseband, the A/D converter 320 need to apply a sample frequency which is higher than or equal with twice an upper edge frequency of the upper frequency band. Circuits for sampling with high sampling frequencies are expensive to manufacture and consume a large amount of power, and therefore it is complex and expensive to provide such sampling circuits. When put into practice, there is complex, or even not possible, to design to multiband receivers for handling substantially separated frequency bands.
There is a need to devise a method for optimising multi-band receivers, and for handling used frequency bands effectively in the multi-band receivers.